1. Field of the Invention
This invention relates to disk drives for flexible or so-called "floppy" disks and, more particularly, to apparatus associated with such drives for protecting the disks against mutilation by improper operation of the disk engagement assembly of the drive.
2. Description of the Prior Art
Floppy disk drive units, or "disk drives", are small information storage systems which are used for information storage in small mini-computers, off-line data terminals and other processors of digital information where low cost, compact storage and processing of relatively limited quantities of digital data is desired. These functions can be, and have been, performed by small tape cassette units. However, floppy disk drives possess certain advantages over the cassette tape drives in that the stored data can be accessed more readily and a considerable advantage in cost is provided, with respect to both the drive unit and the storage media.
A floppy disk drive typically contains a magnetic head for writing and reading data stored on the opposite sides of a flexible disk having magnetic recording surfaces, a positioning motor for positioning the heads for access to the various tracks on the disk, a drive motor for rotating the disk, and associated circuitry for transferring the data in electrical signal form between the heads and the plug interface with associated equipment. The disk drive also typically includes a pivoted access door coupled to a pivoted disk holder plate (carrier) which carries the upper member of a two-part disk engagement assembly. The other disk engagement member is mounted on the drive spindle below the position of the disk when it is inserted in the drive. The disk and its jacket are both provided with central holes, the jacket hole being larger in diameter than the disk hole. The upper disk engaging member is tapered or truncated cone-shaped with the smaller end down and serves to center the disk relative to the spindle as the upper member is moved downwardly through the disk hole into engagement with the spindle-mounted member, in which position it engages the disk against the lower, spindle-mounted member for rotation therewith. The upper disk engagement member and the plate on which it is rotatably positioned are moved toward or away from the disk and spindle by closing or opening the disk drive door to which the plate is pivotably connected.
It will be appreciated that it is essential to protect the disk, as the storage medium, from damage. The loss of a memory disk by mutilation with nearly half a million bytes of data stored thereon can be very crucial. It has been found that the disks as inserted in the drive are not always moved all the way into the operating position. In such a case, closure of the door to lower the disk plate and upper engagement member may serve to move that member down against the disk, rather than into the hole. When this occurs, the portion of the disk immediately surrounding the hole is mutilated and the disk is rendered valueless with an attendant loss of the data stored thereon.
Various systems have been employed to preclude the possibility of operating the disk engagement mechanism when the disk is not fully inserted into the unit. For example, attempts have been made to deal with this problem by interlocking the movable elements coupled to the upper disk engagement member with the disk and its jacket. One such attempt has comprised a switch and solenoid combination. However, such an arrangement is unsatisfactory in that it introduces undue complexity and cost into the system. The arrangement takes up space and consumes power, besides presenting an element of unreliability. Other arrangements have included door-blocking arrangements and the like, all without providing a satisfactory solution to the problem.